In recent years there is a growing usage of wireless connectivity in almost every device. The growing commercial adoption of the “Internet of Things” (IoT) leads to a situation which multiple device and object types are designed to be coupled with wireless transmitters or wireless sensor nodes in order to enable internet communication on one hand, and direct connectivity to other devices or objects on the other hand. In some cases, the objects comprising the wireless transmitters or the wireless sensor nodes can be electronic devices, such as a mobile telephone, a tablet personal computer, and the like. In some other cases, the objects comprising the wireless transmitters or the wireless sensor nodes may be wearables, clothing and apparel items, furniture's, decorative objects, and the like. Communication between objects and devices utilizing wireless communication has a number of usages, however, in some cases the direction/or the physical location of the objects is required. For example, determining the relative direction of a device measuring environmental conditions such as wind velocity or temperature has a considerable importance to the person who receives the information. Furthermore, in case the wireless sensor nodes transmitting the information are associated with a device carried by a person, the relative direction of the device transmitting the information changes constantly. In such cases, real time direction detection is required in order to determine the current relative direction of the device transmitting the information.
Prior art radio transmission and reception systems relate to the human body in what can be categorized as two contrary approaches: whereas one approach relates to the body as an obstacle that needs to be overcome, the other approach relates to it as an antenna per-se. The common factor of many DF techniques is that within the antennas array of the direction-finding device (DF), it is required that all the antennas will have the same free space towards the target, which direction is desired. It does not mean that there always must be a free line-of-sight between the DF and the target—it means that within the antenna array, there should be no absorbing material between the antennas, so they will be able to “see” the same, and based on the pattern radiations to determine the direction of the signal.
There are many methods known for a Radio Frequency (RF) detector to find the direction of an RF source (Target), mainly using wave analysis methods. These methods can be generally categorized as Direction-Finding (DF) techniques and Monopulse techniques.
DF techniques can be categorized in groups—those which find the target's direction based on received signal amplitude, based on received signal phase, based on received signal timing etc.
For the DF techniques described in general hereunder, the signal does not have to be modulated or bear any kind of information, and may be CW (Continuous Wave) or pulse.
Amplitude-based DF techniques use one or more antennas. An example of a single antenna DF is a rotational directional antenna. The direction, from which the Received Signal Strength (RSS) or Received Signal Strength Indication (RSSI) is the highest, is the expected direction of the target.
Amplitude DF which use several antennas measure the RSS/RSSI at each antenna and calculates the AOA (Angle of Arrival) of the signal using the amplitude differences.
Typical examples of amplitude DF that use several antennas are amplitude monopulse, Adcock, etc. Additional techniques assess the distance of the target, based on the signal strength, and by triangulating several measurements calculate the location of the target.
Phase-based DF techniques use two or more antennas and measure the phase difference of the arrival of a signal in the antennas and calculate from these phase differences the AOA of the signal.
This group includes for example interferometer DF, correlative interferometer DF, etc.
Time-based DF techniques are best known as TOA (Time of Arrival) kind of DF. They use two or more antennas and measure the time difference of the arrival of a signal in the antennas and calculate from these differences the signal's AOA. This group includes for example short and long base TOA, DTOA (Differential Time of Arrival) etc.
Monopulse DF techniques mainly used in ELINT (Electronic Intelligence) systems and radars, to find the direction from which a pulsed radar signal or echo is received. The signal is received in two or more directional antennas. The signals in the antennas, usually highly directional antennas, are added in phase to compose a Sum or S signal and added in opposite phase to compose a Difference or D signal, in one or two dimensions, azimuth, elevation or both. Based on the S and D signal strengths, the direction of the target is found.
U.S. Pat. No. 7,323,996 titled “RFID reader having antenna with directional attenuation panels for determining RFID tag location” describes an antenna structure capable of determining the direction of a radiofrequency identification (RFID) tag, which includes a wide-angle antenna disposed within an attenuator that has regions of low attenuation. The attenuator may include a metal plate with holes. In this case, the antenna only detects RFID tags that are aligned with a hole, and hence the direction of the RFID tag is detected.